Although various kinds of sliding switches are normally used at about from -30.degree. C. to +80.degree. C., the temperature of a copper contact increases to about 160.degree. C. quite often, said copper contact being widely used from a viewpoint of cost in a switch attached directly to an engine chamber of automobiles, aircraft and the like, a change-over switch of heater or heating element, and control switch or connector used in an unattended factory. For this reason, usual greases are not adequate for use under these circumstances.
For example, a grease containing lithium salt of higher fatty acid as a thickner increases the electrical contact voltage drop between the copper contacts because the lithium salt (lithium stearate) is oxidized to a varnish solid when the temperature of the contacts increases to 130.degree. C.-160.degree. C. Although commercially available greases comprising polyol hindered esters as a base oil which are developed for a jet engine operated at a condition of low and high temperatures such as "Nye Rheolube 789 DM" (William F. Nye Inc., United States) can be generally used at from -40.degree. C. to +150.degree. C. and produce only a small amount of carbonized residue when they are heated under high temperature conditions such as electric arc, they oxidize the copper contacts remarkably and increase electrical contact resistance under the condition of 140.degree. C./40 H.
In view of the aforementioned situation, the present invention is carried out in order to provide a durable grease for copper electrical contact which is fit for use under the condition of low and high temperatures ca. -40.degree. C.-ca. +160.degree. C.) and much moisture and which not only does not corrode the copper contact but also does not bring about increased electrical contact resistance caused by its deterioration with the passage of time, said grease giving good durability to the electrical contact under arc generating conditions as a result of the small amount of carbonized residue.